Embodiments of the present invention relate to an inductive power providing system and, more particularly, to a power system for providing wireless power to a moving subject via inductive power means.
Generally, medical researchers are working to better understand various aspects of the human body and apply that knowledge to diagnose, prevent, and/or treat a large variety of diseases. Even though the ultimate treatment target are humans, due to complexity, cost, and even ethical reasons, medical researchers often use other subjects to conduct their research/experiments. Oftentimes, researchers use animal models for their subjects. Like humans, the use of large animals, such as primates, dogs or cats are not justified in many experiments. As a result, a large number of medical researchers are interested in conducting experiments on small animal models, such as rats, mice, guinea pigs, fish, aplysia, and the like.
Conducting research on small animals imposes certain challenges and limitations. Long-term continuous measurement of physiological parameters, such as temperature, cardiac rhythm, brain waves, neural spikes, blood pressure, body fluid chemicals, and the like, are more difficult in small animals (than large animals or humans), because they do not carry the same weight of conventional instrumentation on their bodies, particularly when compared with humans. Other than measurement, there are other types of research that require long-term electrical stimulation or injection of a drug in response to a cue or on a regular, predetermined basis, which also are limited when using a small animal as the source. When these animals are tethered or highly confined, the experiment may be biased. This is particularly the case in behavioral neuroscience research experiments, where the natural behavior of the animal in an enriched environment is significant.
In one example, neuroscientists study the functional organization of vertebrate and invertebrate nervous systems in the hope that the knowledge can aid in the prevention, diagnosis, and treatment of disease and dysfunction in the human brain. In vivo electrophysiology has been a powerful tool in pursuing that goal. It has provided data on areas ranging from the organization of primary visual cortex to neural correlation of working memory in the prefrontal cortex. Data from in vivo electrophysiology has helped in the treatment of disorders, including but not limited to schizophrenia, epilepsy, and depression. Many of these discoveries have been made in large experimental animals (e.g., non-human primates and cats) that were either anesthetized or highly restrained, and this approach continues to be productive. Many experimental questions, however, require awake and freely-moving subjects in enriched natural environments. Logistical constraints, cost, life-span, and housing often necessitate using small animals, particularly rodents. The increased importance of genetically-altered mice further highlights the utility of recording in small experimental animals, particularly without the need of removing the power source (battery) for recharging purposes.
Most conventional wireless recording systems for reading and obtaining neural signals involve powering a headstage, which may include analog/digital data conversion and wireless transceiver blocks, with batteries. Batteries add to the size and weight of the wireless system, which is carried by the animal body. For example, animals often carry the wireless system on the head to eliminate damage from chewing, which limits the size of the system leaving less room for the electronics that perform the main tasks. Users and designers of such systems always have to make a compromise between the duration of the experiment and how much payload the animal can carry on its head before it affects its normal behavior. Depending on the complexity and power consumption of the wireless system, this tradeoff limits the duration of each trial to only one or two hours on average before the battery needs to be recharged or replaced. Implantable versions, which should be a few times smaller and lighter, may not even run for an hour before requiring a recharge.
Most neuroscientists, however, particularly those who record from the central nervous system through multiple parallel channels and may have to deal with large volumes of data, forgo the freedom and benefits of wireless data acquisition and tie their animals to large electrophysiology instrumentation with cables. As a result, they face several limitations. A first exemplary limitation is the limited range over which an animal can traverse can be only as large as the cable length permits. Hence, most recording studies in freely moving animals use a relatively small area (typically less than one square meter). A second exemplary limitation is that the cables can double as antennas and pick up electromagnetic noise and interference making it necessary to shield the cage and move the instrumentation further away from the signal source (the animal), which can exacerbate the problem. A third exemplary limitation is that the cables also introduce motion artifacts, particularly when their connectors wear off over time. A fourth exemplary limitation is the need for an unobstructed clearance between the headstage and the data acquisition system prohibits studies in which the animal is allowed to enter enclosed chambers. A fifth exemplary limitation is the weight and sheer stress that the cables add, at least in part to the amount of weight that must be supported by the animal. The cables also induce psychophysical distress and may bias the animal behavior. A sixth exemplary limitation relates to studies that involve more than one animal, which are not feasible in hardwired systems due to the likelihood of cables becoming entangled. A seventh exemplary limitation is that many in vivo recording studies require a commutator to deal with the twisting forces exerted on the cable. Motorized commutators are quite expensive and are potential sources of audio and radio frequency noise. Nevertheless, they are commonly used in setups with a large number of recording and/or stimulation channels.
There have been several recent attempts to develop inductively powered recording systems for batteries in wireless systems. Each of these attempts has stumbled across technical issues that prevent them from being practically applicable, for example and not limitation, to neural recording. For example, one exemplary system proposed an array of nine coils, each 5×5 cm2, at the bottom of a cage to power an implanted 6×6 mm2 coil. This system faced large voltage variations (between 4 and 21 V) as the animal moved around the cage. Hence, there was a significant change in magnetic flux density at the edge of the adjacent coils. Also, the heat dissipation was excessive since all the coils were continuously on. Another exemplary system demonstrated an implantable stimulator and powered it in a chamber surrounded by three sets of coils in three dimensions. The system had an open-loop design, and the size of the chamber was limited to 17×16×16 cm3. Consequently, the animal was quite constrained in terms of the range over which it could move. Yet another exemplary system demonstrated a narrowband wireless system for measuring blood pressure with closed loop power. This system limited the animal movements to a small cage. In another exemplary system, a commercial telemetric device, called VitalView, developed by Mini Mitter Inc. (Bend, Oreg.) is limited to 56×29 cm, and its bandwidth suits low frequency biological signals such as body temperature or heart rate.
Accordingly, there is no currently available system that is suitable for, among other things, neural interfacing in small behaving animals.